Hi. I've started a Slack for Safari extension developers! Email me for an invitation: slack at lapcatsoftware.com
The purpose of this Slack is mutual support for Safari extension development on iOS and/or macOS.
Apple engineers who work on Safari extensions are welcome too!
Update: This Slack channel has been shut down. There was a lot of initial interest, but it never really caught on, and it was mostly quiet after the first couple of weeks.
If the Developer Forum moderators could delete my post, I'd appreciate it. I can't seem to do it myself.